1. Field of the Invention
The present invention relates to a shift drum apparatus that changes a gear position of a transmission mechanism. In particular, the present invention relates to the structure of the shift drum which is configured to include, as separate members, the shift drum main body and the lid member.
2. Description of the Background Art
In a transmission mechanism in which a shift drum apparatus is used to change a gear position of a transmission, a cylindrical shift drum that rotates to slide a shift fork well known. In addition, it is well know to manufacture the cylindrical shift drum through casting. In the known transmission, a gear position sensor, which detects the currently selected gear position by detecting an amount of rotation of the shift drum, is connected to an end face on a first end of the shift drum in a cylindrical axis direction. The portion of the end face of shift drum, to which the gear position sensor is connected, is also formed integrally with the shift drum. Such a transmission mechanism is disclosed, for example, in Japanese Patent Laid-open No. Hei 7-230741. Such a shift drum includes a hollow portion at a center thereof for weight reduction. The hollow portion is formed by using a core during casting.
By integrally forming the shift drum through casting as described above, however, attempts to thin the wall of the shift drum to achieve weight reduction might result in a mold shift or similar problems. If such a problem occurs, the wall thickness can become partially excessively thin, resulting in failure to achieve sufficient drum strength for connecting the gear position sensor. There is therefore a problem in that the inability provide a cylinder having a thin the wall results in an increased weight of the shift drum, which, in turn, results in an increased weight of the entire shift drum apparatus.
It is therefore an object of the present invention to provide a shift drum apparatus that is reduced in weight.